The present invention relates generally to drive circuits that are used to control the delivery of high power levels to high power loads, such as motors, and, more particularly, to an independent safety processor for disabling the operation of high power devices.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
High power devices are commonly employed in a variety of environments including, for example, industrial facilities and construction environments. High power devices generally include a variety of different devices including, for example, motors and heating devices. Although the operation of such devices under normal conditions does not pose undue risk, there are circumstances in which such devices must be reliably disabled so as not to pose risks to human beings or other devices.
For example, high power motors often rotate at high speeds and/or provide significant torques that in certain situations could pose risks to human beings or other devices that come into contact with the motors themselves or with other devices coupled to those motors. In particular, when such motors or devices coupled to those motors are replaced, fixed, modified, tested or otherwise operated upon by human beings such as engineers or service technicians, it is desirable that the motors be reliably disabled such that the motors cease to rotate or deliver sustained torque.
In view of the possible hazards associated with high power devices generally, many modern industrial and other facilities employ various electronic and other technologies that reduce the risk of accidents and enhance overall system safety. Additionally, standards have been developed with a goal of further reducing the risk of accidents. For example, with respect to industrial facilities, standards from organizations such as the NFPA, ISO, CEN, CENELEC, and the IEC have been developed to establish requirements for safety. The technologies used to enhance system safety often are designed to comply with, or to assist in making a facility compliant with, standards from one or more of these organizations.
Some of the technologies employed to enhance system safety are designed to reliably disable high power devices. For example, technologies such as high power contactors are often used to couple and decouple the driven devices to and from their high power drive circuits. Such contactors often include multiple, redundant high power contacts that are physically coupled to one another in such a way that, if one or more of the contacts become locked/welded in position, a signal is provided indicating that a fault has occurred. The signal can be, for example, the turning on of an indicator light at an operator interface or simply the failure of the high power device to start operating when commanded to do so.
Such high power contactors are often used because of their relative technical simplicity and reliability. Nevertheless, high power contactors are disadvantageous insofar as they are relatively expensive, and physically large and bulky. Further, in certain circumstances, the disconnecting and connecting procedures for implementing these high power contactors can be complicated and/or time consuming. Consequently, the implementation of such high power contactors can negatively impact the overall efficiency of an industrial or other system in which the high power devices are employed.
Because of these disadvantages, efforts have been made to find other mechanisms that could be used to disable high power devices. One alternate method of disabling a high power motor that has been attempted, for example, has involved disabling high power transistors of a drive circuit that deliver the high levels of power to the motor. However, this method has thus far proven to be insufficiently reliable.
Some safety systems employ a safety relay that when engaged locks out operation of the high power device. Such systems, however, are susceptible to a single failure of the safety relay compromising their safety function.
Therefore, it would be advantageous if a new mechanism could be developed that allowed for reliable disabling of high power devices such that the high power devices could not inadvertently start operating in a manner that might present a hazard. In particular, it would be advantageous if the new mechanism could provide a level of redundancy greater than a single failure and provide for detecting failures to increase the safety integrity level. Further, it would be advantageous if the new mechanism was relatively easy and inexpensive to implement.